SUMMARY Chronic pancreatitis (CP) is a disease associated with inflammation and progressive destruction of the secretory pancreatic parenchyma. Risk factors and processes such as in?ammation, necrosis, apoptosis or duct obstruction contribute to pathogenesis in pancreatitis. Pathologic features of the disease often involve chronic inflammation with variable pain, calcifications, necrosis, lipomatosis, fibrosis and other complications such as diabetes or even pancreatic cancer. Most pancreatitis cases are classified as acute pancreatitis (AP), recurrent acute pancreatitis (RAP) or CP. AP and CP represent a disease continuum usually involving RAP as an intermediate step. Substantial morbidity and even mortality are common features in CP, and chronic alcohol consumption or genetic risk factors can instigate the progression of a sentinel attack of AP to RAP and ultimately CP. The onset, progression and severity of CP are unpredictable and most patients with risk factors do not develop pancreatitis (i.e., heavy alcohol users). Major challenges to overcome include the need to develop new strategies for patient evaluation, to predict disease etiology and progression, and to apply personalized interventions. Genome-wide association studies (GWAS) on pancreatitis identified polymorphisms at the X- linked CLDN2 locus associated with RAP and more prominently with alcohol-related CP in North American patients of European ancestry. These findings were later replicated in a study that reported association of genetic variants in CLDN2 with CP in Indian patients. CLDN2 encodes a tight junction (TJ) protein (claudin-2) that forms paracellular channels for small cations and water. Claudin-2 is expressed in ?leaky? epithelia such as the proximal nephron and the small intestine. Claudin-2 expression is upregulated in the small and large intestine in inflammatory pathologies (e.g., Crohn?s disease) and infectious diseases, and this condition contributes to produce diarrhea via a leak flux mechanism. With the exception of a few studies reporting low expression of claudin-2 in ductal cells and islets in the mammalian pancreas, there is no information on the role of this protein in pancreas physiology. Similarly, there are no published reports on possible changes in claudin-2 expression in the pancreas under pathologic conditions, the effects of claudin-2 deficiency in ductal function, or mechanisms that regulate claudin-2 pancreatic expression. Addressing these important issues is necessary to understand poorly studied yet relevant aspects of pancreatic ductal physiology. This proposal will use loss-of-function approaches, mouse models, pancreatic ductal cell cultures, and single cell RNA sequencing (scRNAseq) methods, to begin dissecting the role of claudin-2 in pancreatic tissues in normal and pathologic conditions. The long-term objective is to validate our findings in mice in human pancreatic tissues and to use the information to understand how CLDN2 variants affect CP outcome in patients.